Here's the complete story, now that I can easily post the photos...
I used a leftover deck from my nephew's build (finished in 2013), and used some Cabosil thickened epoxy to stick the foam on an edge. I then wrapped the CF bias woven tape around the foam, and wet out the CF. I had barely any resin left in the tray, so I may have starved the CF.
This is what I started with
I cut the deck piece into two 2" wide strips, one just the previously laminated deck, the other side with the foam and CF tape. I kept the wood and glassed parts the same 2" width, so any differences in strength and/or stiffness could be attributed to the gunnel section only.
Here's how they looked from the end...that's a Starrett 12" rule in the photo, just for a reference.
Then I put the baseline section (glass/cedar/glass only) in a little load frame. I operated in load control and used a 10 lb setpoint. Here is the baseline section at about the max load.
After doing the baseline load-deflection test, I put the sample gunnel section in the load frame and repeated the test. It was quickly apparent that I needed more than 10 lb load, so I increased the setpoint to 25 lb. Here is the CF and foam gunnel at the max load. Look carefully and you'll see a laminate failure on the compression side. I attribute that to my negligence, or maybe laziness when I didn't use enough resin the wet out the CF properly. (hint, the failure is about an inch to the left of the applied load)
And here's a comparative plot of the baseline hull section and the CF gunnel section.
If anyone wants to verify my numbers, here they are. The distance between the supports was 11 15/16 inch, max loads were 10 and 25 lbs, for the baseline and CF gunnel respectively. Deflections were 0.773 inch and 0.628 inch. Interestingly, the baseline section had no hysteresis, the CF, with the compressive failure, had a huge hysteresis loop!!
And here are the details on the baseline substrate...cedar was .12 thick with single layer 4 oz cloth on each side, for a total thickness of .13 inch. Width and length was 2.0 x 14 inch. Foam substrate was 0.75 x 0.75, with a 0.25 radius 2x, and a 0.13 x 0.50 groove. Baseline weight was 0.085 lb and gunnel section was 0.155 lb.
What does all this mean?? How do I know?? OK, maybe I know...From these first indications, that single layer of CF over the foam could be sufficient, assuming:
1. There is a complete bond between foam and hull in the groove.
2. There is solid contact between the CF tape and the foam and hull.
3. The CF tape is fully saturated.
Now, I did order some 4" glass tape, I'm a belt and suspenders sort of guy.
I am pleased though, with the look of the CF tape...it will be very easy to keep a clean, straight line, and resin drips should not be an issue. The black CF tape contrasts nicely with the cedar, and I expect it will look even better against the red pigmented resin.
Well, guys, what say you??
